I've never heard of a "down-graded" 430cid.

Take a look at the MEL Engine Forum link. Someone spent allot of time compiling this post on the MEL engine. Set aside some time to read it.

As for the Thunderbird 430, seems like the dust had settled by the time this engine was going into the TBird and the refinements had been made.

430 ID help

Thanks for posting that, Ken! I have added that link to the 430MEL Engine section of the Technical Resource Library, with proper credit. Good stuff!

"down graded 430"

meant less compression, milder cam,smaller valves. you of all people should now all of this, being an expert!!(kidding)

Thankyou

I just want to thank all you guys for the effort and great help I have recieved! You guys are great!! My dad had an early '58 Monterey, Modified 383, 312 HP. I could beat any 390 or 348 for top-end. That red ribbon speedometer was great to see it all the way to the right at over 130 MPH! I was stationed in Rantoul, illinois at the AFB in 1965, 600 miles from home. I used to leave on Friday after noon to get home in Iowa. One time I was getting on I-80 ,just north of Rantoul. the sign said 110 miles to Davenport, Iowa. I put that Merc down the interstate and never let it get under 100 MPH. I made it to davenport in an hour. Man that was a **** of a good engine. Never did hurt it.Thanks again,.

I believe it was assembled Nov 28, 1958 and falls under #3 below.

You would need to check individual component date codes to be sure of what you have, but I believe you would have the basic 383 Mercury head installed (referenced in the literature as #5750062 but in reality is observed as #5750063). This was a factory change to the 430 that was implemented on 1/9/58.

1959 heads had 45 degree intake valve seats whereas 1958 had 30 degree. That change presumably happened after your engine was assembled.

The block deck height was increased 0.020" on 2/17/58 which reduced compression to 10.0.

1-big valve, high 10.5 compression engine (from around 9/1957 to 1/8/1958)
2-small valve, high 10.5 compression engine (from 1/9/1958 to 2/16/1958)
3-small valve, lower 10 compression engine (from 2/17/1958 onward)